Mn/DOT scanned their archives (minus two editions) for the Minnesota Digital Library. If I ever get around to playing in an image editor to stitch the two files together, I have most of the old Michigan maps in electronic form that were scanned by the Library of Michigan. (The maps were larger than the drum scanner, so they had to get them to me in two passes each.) I can legally put pre-1958 online since the Michigan State Highway Department didn't copyright their maps before that year.)